1. Field of the Invention
The present invention relates generally to temperature sensing and, more particularly, to an apparatus and system for sensing a temperature of a surface of an object.
2. Description of Related Art
Certain objects, such as chemical reaction vessels, require careful temperature sensing over one or more of the surfaces of the object. For example, in a chemical reaction vessel, certain portions of the surface may reach hazardously high temperatures when certain reactions take place within the reaction vessel. If the hazard is not identified, and the reaction is not controlled, a catastrophic breach of the vessel may occur. Furthermore, the exact surface or location on the surface where hot spots occur may be unpredictable.
One method of monitoring surface temperatures is distributed temperature sensing using optoelectronic devices attached to fiber optic cables. In typical distributed temperature sensing systems, the fiber optic is wrapped around an object, such as a reaction vessel, in a single continuous helical coil. For example, the temperature sensor described in U.S. Pat. No. 5,821,861 to Hartog, et al. describes a fiber optic temperature sensor wrapped around a reactor vessel in a continuous helical coil. A continuous helical coil is not ideal because it may be difficult to install and secure a helical coil to a large or complex surface.
The typical distributed temperature sensing system uses thermally conductive cement to affix the fiber optic cable to the surface of the object. Unfortunately, the surface of the object and the thermally conductive cement or fiber optic cable may experience differential thermal expansion. Specifically, the surface of the object may expand more rapidly, or less rapidly than the cement or fiber optic cable. In such situations, the differential thermal expansion may cause the thermally conductive cement to sheer from the surface of the object. This sheering effect may reduce thermal coupling between the surface of the object and the fiber optic cable. In typical situations, the fiber optic cable may become dislodged from its proper position, making temperature readings unreliable and reducing overall system performance.
Published U.S. Patent Application No. 2006/0115204 to Marsh et al. also describes a common distributed temperature system. However, Marsh only describes a small improvement on a typical system. The improvement involves the use of reference coils at certain predetermined locations on the fiber optic cable. The reference coils described in Marsh provide an optoelectronic reference point on the cable for applications where the length of the fiber optic sensor cable actually measuring the temperature of an object of interest is small with reference to the overall length of the fiber optic cable. The reference coils do not physically separate the coil, but provide optoelectronic reference points to electronically isolate a portion of interest from an entire fiber optic cable. This improvement on prior systems does not address the problem of sheering thermally conductive cement caused by differential thermal expansion, or the difficulties involved with helical wrapping of objects.